A polycarbonate resin has a high refractive index and excellent transparency and impact resistance and is recently widely used as a raw material of lenses, particularly a raw material of spectacles lenses. Spectacles lenses made of the polycarbonate resin are thinner, lighter, safer due to significantly high impact strength, and more functional than conventional spectacles lenses and plastic lenses formed by cast polymerization (hereinafter referred to as “cast lenses”). Therefore, they have been increasingly used as vision corrective lenses, sunspectacles lenses and safety spectacles lenses.
Recently, it has been strongly demanded to impart ultraviolet absorbability to spectacles lenses so as to protect the eyes from harmful ultraviolet radiation. For example, cast lenses and spectacles lenses meet the demand by forming a coating layer having ultraviolet absorbability on the surface of the lenses. However, the coating method has a problem of an increase in product cost and a problem of slight yellowing of the lenses. Further, in the case of the cast lenses, an ultraviolet absorber is added at the time of polymerization. However, this method has a problem of inhibition of polymerizability and a problem of significant yellowing of the lenses.
Meanwhile, in the case of the spectacles lenses made of the polycarbonate resin, the polycarbonate resin itself has ultraviolet absorbability, and since the polycarbonate resin is a thermoplastic resin, any ultraviolet absorber can be contained therein easily if the ultraviolet absorber is added at the time of melt molding. It is particularly desired to contain an ultraviolet absorber of long wavelength side. However, the conventional polycarbonate resin is not capable of absorbing ultraviolet radiation of longer than 375 nm by itself, and if it is desired that the resin absorb longer wavelengths than 375 nm, a large amount of an ultraviolet absorber must be added. Ultraviolet absorbers are generally sublimable. Thus, when a large amount of an ultraviolet absorber is added, the ultraviolet absorber sublimes and contaminates a mirror-surface mold upon injection-molding of the polycarbonate resin and significantly damages the appearance of a lens to be obtained accordingly.
In Japanese Patent Publication Nos. 6-035141 and 6-041162, a method is described that comprises adding 0.1 to 20 parts by weight of oligomer-type ultraviolet absorber which hardly sublimes to 100 parts by weight of polycarbonate resin and forming the surface layer of a multilayer laminated sheet or film from the resin at the time of extrusion of the sheet or film. However, its object is to impart weather resistance to the sheet and not optical. Further, some ultraviolet absorbers are capable of absorbing ultraviolet radiation of even longer wavelengths. However, since a polycarbonate resin is yellowed significantly by addition of these ultraviolet absorbers for absorbing long wavelengths, a large amount of a bluing agent needs to be added to eliminate a yellow tinge. However, this method has a problem that when the polycarbonate resin is used for forming lenses, the transparency of the lenses is impaired by a large amount of the bluing agent, and this method can only provide significantly opaque lenses having low luminous transmittance.
Further, Japanese Patent Laid-Open Publication No. 7-092301 proposes a plastic lens which contains an ultraviolet absorber and an infrared absorber to prevent transmission of ultraviolet radiation and near-infrared radiation. However, lenses obtained by this method have unsatisfactory transparency.
Meanwhile, Japanese Patent Laid-Open Publication No. 62-146951 describes a polycarbonate resin composition having light resistance improved by containing 0.001 to 5 parts by weight of alkylidene bis(benzotriazolylphenol) compound represented by a specific structural formula based on 100 parts by weight of polycarbonate resin. This patent publication indicates the results of preparing test pieces by adding 0.30 wt % of the above 5 specific compounds to polycarbonate resins, irradiating the test pieces with ultraviolet radiation by a high-pressure mercury lamp and measuring the degree of yellowness of the test pieces and changes thereof (ΔYI). The results merely indicate that the changes in the degree of yellowness were decreased by addition of the above specific compounds.
Japanese Patent Laid-Open Publication No. 4-292661 describes a resin composition containing 0.01 to 0.15 parts by weight of ultraviolet absorber having an absorption maximum at a wavelength of 280 to 360 nm and no absorption at a wavelength of 400 nm based on 100 parts by weight of transparent thermoplastic resin including a polycarbonate resin. Since a silver salt film formed from this resin composition has a sensitivity peak at a wavelength of 400 nm, the film has been developed for a camera lens having a transmittance of light having a wavelength of 400 nm of not lower than 80%.
Further, Japanese Patent Laid-Open Publication Nos. 9-263694 and 9-291205 describe a resin composition containing an ultraviolet absorber having an absorption maximum at wavelengths of 300 to 345 nm and 346 to 400 nm based on 100 parts by weight of transparent thermoplastic resin including a polycarbonate resin. Although this composition has been developed for a spectacles lens having excellent transparency and high ultraviolet absorbability, it shows a significant change in hue and unsatisfactory molding heat resistance when subjected to heat history such as re-extrusion to recycle product wastes.
Further, Japanese Patent Laid-Open Publication Nos. 2003-231803, 2003-231804 and 2003-231805 describe a resin composition containing 0.003 to 1 part by weight of specific benzotriazole-based ultraviolet absorber and benzofurano-2-one type compound based on 100 parts by weight of aromatic polycarbonate resin. Although this composition is a resin composition having an improved balance in between hydrolysis resistance, impact resistance and a mold staining property, it has poor hue and also shows a significant change in hue and unsatisfactory molding heat resistance when subjected to heat history such as re-extrusion.